This application is based on and claims priority to Japanese Patent Application No. 2000-362211 filed Nov. 29, 2000, the entire contents of which is hereby expressly incorporated by reference.
1. Field of the Invention
The present invention generally relates to an exhaust system for an internal combustion engine. More specifically, the present invention relates to an air injection system for the exhaust system of an internal combustion engine, which can be used in a watercraft.
2. Related Art
In order to control the emission of unwanted exhaust gas constituents, a wide variety of devices have been proposed. Frequently, catalytic converters are employed for treating exhaust gases emanating from internal combustion engines before those gases are discharged to the atmosphere. As is well known, a catalytic converter should be operated at the appropriate temperature in order for it to effectively treat exhaust gases.
For this reason, it has been proposed to place the catalytic converter as close to the exhaust ports of the engine as possible. However, a single catalytic converter is not always sufficient to provide all of the desired exhaust gas treatment. Therefore, it has become common to employ plural catalytic converters in series in an exhaust system.
Where plural catalytic converters are used, the downstream catalytic converter will receive exhaust gases that have been previously treated. A catalytic converter, in effect, causes afterburning of the exhaust gases which provides one way in which unwanted exhaust gas constituents are controlled. However, the downstream catalytic converter may not receive exhaust gases that are adequate to permit further afterburning.
It has also been known to add supplemental air to exhaust systems between the upstream and downstream converters so that the downstream converter can effectively treat the exhaust gases. One way in which this is done is to provide an atmospheric air inlet to the downstream catalytic converter which will introduce air to the converter so as to allow more effective afterburning. For example, in the art of automotive internal combustion engines, it has been known to drive an air pump with a crankshaft so as to draw and pressurize air in the vicinity of the engine and inject the air into the exhaust system in the vicinity of the exhaust ports of the engine and/or at a position between two catalytic converters mounted in series. In one known system, air from an air pump passes through a one-way check valve and then is divided into individual air supply lines for feeding each exhaust port with secondary air. Other known systems include an additional secondary air supply line with a check valve, which feeds secondary air to a point in the exhaust system between two catalytic converters mounted in series.
One aspect of the present invention includes the realization that prior known secondary air injection systems have suffered from several problems. In particular, as an internal combustion engine operates, air fuel mixture is burned inside the internal combustion chambers. The burnt mixture is then discharged to the atmosphere through the exhaust system. However, because the exhaust gas is forcibly discharged from the combustion chamber, the pressure inside the entire exhaust passage tends to be positive and to fluctuate at a frequency corresponding to the number of combustion chambers within the internal combustion engine as well as the engine""s speed. Thus, it has been found that prior known secondary air injection systems do not accurately inject the proper amount of secondary air into the exhaust system.
In accordance with another aspect of the present invention, an engine includes an engine body defining a plurality of combustion chambers. The engine also includes an exhaust system configured to guide exhaust gases from the combustion chambers to the atmosphere. The exhaust system includes a plurality of exhaust runners extending from the engine body and merging into a common passage. A secondary air injection system includes a plurality of secondary air conduits configured to deliver secondary air separately to each individual exhaust runner, and at least one check valve is disposed in each secondary air conduit.
By constructing the engine as such, the check valves attenuate the effect of exhaust gas flow in one exhaust runner on adjacent exhaust runners. Thus, the secondary air injection system of the present engine can more accurately deliver secondary air to the exhaust system, and thereby enhance the cleaning effects of secondary air injection.
In accordance with yet another aspect of the present invention an engine includes an engine body defining at least one combustion chamber. The engine also includes an exhaust system defining an exhaust discharge path extending from the engine body to the atmosphere. A catalyst device is disposed in the exhaust discharge path. A secondary air injection system is configured to inject secondary air into the exhaust discharge path at a position upstream from the catalyst device. Additionally, a cooling jacket is disposed in thermal communication with at least a portion of the exhaust discharge path upstream from the catalyst device and downstream from the position into which secondary air is injected into the exhaust discharge path.
By constructing the engine as such, the cooling jacket helps to cool the exhaust gasses which can be heated by the injection of secondary air. Thus, the present engine helps prevent over-heating of downstream exhaust components such as, for example, but without limitation, the catalyst device.